1. Field of the Invention
The present invention relates to an apparatus for melting off a glass part from a hollow glass object, especially to form a non-circular cut surface, which includes a burner device arranged around the hollow glass object, a holding and rotating device, in which the hollow glass object to be melted off is held fixed and by which it is rotated, and a control device for controlling the melting off of the glass part from the glass object by means of the burner device.
2. Prior Art
Hollow glass bodies are made by blowing glass, either by machine or by hand. A glass blank is produced, which has a glass top part with a glass ring besides the form of the desired article. This top part of the glass blank resulting from the manufacture must be cut away in a subsequent process from the actual desired glass product.
A method usually used for this separation process in the hollow glass industry is hot melting off by means of a gas/oxygen burner. A work tool holds the glass blank and rotates it about its own axis, while a stationary annular burner, e.g. a burner whose nozzles are arranged in a circle, with a predetermined spacing from the glass surface heats the glass, until the glass top part with the glass ring drops off. The rotation of the hollow glass blank is necessary in order to compensate for nonuniformities in the heat distribution due to, for example, a clogged nozzle. The hollow glass object is normally clamped in such a way that the glass top part points downward and can drop downward with the help of drawing tongs which grip the glass top part.
A sufficient quality for the separation process is only achieved when the spacing between the hollow glass object and the burner nozzles is maintained constant around the entire circumference. Otherwise the glass top part releases only in a non-uniform manner from the glass object or blank and the cut edge of the glass product thus formed is deformed and irregular.
This is no problem for hollow glass objects whose cut surface is circular. However it is not possible to separate the glass top part from a hollow glass object to form a non-circular cut surface with the standard hot melt off. Hollow glass objects that have a non-rotationally symmetric shape, especially oval or triangular, have a non-circular cut surface. A non-circular cut surface is also produced from a rotationally symmetric hollow glass object with a circular cross-section, which is not held in the holding device so that it is perpendicular to the central axis of the circular burner device. Instead it is held inclined to the central axis in the holding device. Then the cut surface is elliptical.
Currently in the case of a hollow glass blank from which a glass top part is melted off to form a non-circular cut surface, the glass top part is cut off with the help of a diamond grinding disk and subsequently the cut edge of the hollow glass blank is fused or ground smooth. This type of separation is disproportionately expensive and can make the final product very expensive.
JP H01-270526A suggests using a burner device whose burner nozzles are arranged so that they correspond to the shape of the cut surface. This generally has the disadvantage for non-circular cut surfaces that, on the one hand, a special burner is needed for each cut surface shape and size and that, on the other hand, uniform melting cannot be guaranteed, since the hollow glass object and burner device cannot be rotated relative to each other.
It is an object of the present invention to provide an apparatus with which a glass part can be hot-melted off from an arbitrarily shaped hollow glass body, object or blank to form a non-circular cut surface, without after-working the cut edges.
This object, and others which will be made more apparent hereinafter, are attained in an apparatus for melting off a glass part from a hollow glass object, especially to form a non-circular cut surface, which has a burner device arranged around the hollow glass object, a holding and rotating device, in which the hollow glass object to be melted off is held fixed and by which it is rotated, and a control device for controlling the melting off of the glass part from the hollow glass object by means of the burner device.
According to the invention, the burner device includes burner sections attached movably in a cutting plane around the glass object so that all burner sections can be always arranged at a constant distance from the exterior surface of the hollow glass object with the aid of the control device.
The present invention is based on a division of the conventional annular burner device into a plurality of individual burner sections and mounting the burner sections, so that they are movable or adjustable. A burner section includes at least one burner nozzle. The positions of the burner sections in the cutting plane are adjustable. They can be controlled individually by the control device. They are controlled so that all of them always maintain a constant spacing from the exterior surface of the hollow glass object during the entire melting process. For that purpose information must be stored in the control device regarding the location of each individual point on the outline of the cut surface as a function of the rotation angle in the cutting plane.
The apparatus according to the invention can be adjusted for each arbitrary cut surface, since only information regarding the location of the points on the outline of the cut surface changes. If necessary, the number and dimensions of the individual burner sections can be adjusted. This is however only necessary with strongly varying cut surfaces. The apparatus according to the invention thus allows arbitrarily shaped hollow glass bodies to be cut into two parts at any arbitrary plane by hot melting off by means of a burner. This cutting off happens now in only one step and not in two steps, as in cutting separations with a diamond grinding disk and subsequently with thermal fusion treatments. Because the burner sections are always held at the same constant distance from the hollow glass object, the glass melts uniformly and the cut edge does not need to be further worked after separation of the parts from each other.
In a preferred embodiment the control device has at least one template and a mechanical coupling device arranged between the at least one template and the burner sections. The template contains the information regarding the position of the points on the outline of the cut surface of the hollow glass blank in the cutting plane. The mechanical coupling device scans the template and divulges the location information controlling to, i.e. appropriately adjusts and guides, the burner sections, since the mechanical coupling device can change the distance of each burner section to the hollow glass surface.
Other control devices could, for example, be processor-assisted or have a template, which is scanned optically, whereby the optical signal controls the burner sections.
Preferably at least one template with the same rotation axis as the hollow glass object is attached in the holding and rotating device and is rotated like the hollow glass blank with the same angular speed. It is still advantageous when the outline of each template is equal to the outline of the cut surface of the hollow glass blank. In that case the embodiment of the mechanical coupling device is kept as simple as possible, since the mechanical coupling device can communicate the position information in the template 1:1 to the burner sections. For example, no longitudinal transformation by means of special conversions is needed.
In a preferred embodiment the individual burner sections are movable together with each other. The individual burner sections are connected with each other by means of a pivot joint, so that they are movable in the cutting plane relative to each other. Thus the pivot joints do not necessarily need to be added to the burner sections, but can be found on the mechanical coupling device for the burner sections with the template.
The mechanical coupling device between the template and the individual burner sections preferably comprises a respective rod attached to each burner section, which has at least one roller for traveling on the template circumference a on its end opposite the burner section. If the burner section is spaced a short distance from the hollow glass object and the template rotates a bit further, so that the burner section now has an additional spacing from the burner section, the template presses the rod further from the rotation axis of the template by means of the roller. Since the rod is rigidly connected with the burner section, it transmits this spacing change to the burner section. In this embodiment it is appropriate when the template is directly attached over the hollow glass object and has the same rotation axis.
Preferably plural burner sections are assembled in subsections, which are engaged with template. Because of this feature it is guaranteed that the burner sections have a constant spacing from the hollow glass surface.
In order to stabilize the system of. mechanical coupling, an additional embodiment of the invention has two templates with equal circumferences arranged one above the other. In the case of mechanical coupling by means of a rod, two rollers are attached to this rod. While the two rollers travel around the templates, possible jumping or release of one of the templates from its roller guiding it is prevented.
It has proven to be especially advantageous to form the apparatus from two parts which complement each other, for example two half frames, which are pivotable away from each other and on which the burner device with its burner components is mounted. Because of this feature it is possible to pivot away half of the burner sections, so that one has better access to the hollow glass object or body and it can be clamped more easily in the holding and rotating device.